SEOUL, July 26 (Reuters) - North Korea said on Friday its latest missile launch was a warning to South Korean "warmongers" to stop importing weapons and conducting joint military drills, a message analysts said was also aimed at the United States.

North Korean leader Kim Jong Un personally watched the test-fire of two short-range ballistic missiles on Thursday, the first test since Kim met with U.S. President Donald Trump last month and agreed to revive denuclearisation talks.

The missile test raises doubts about the revival of denuclearisation talks, which stalled after the collapse of a second summit between Kim and Trump in Hanoi in February.

Trump, speaking to reporters at the White House later on Friday, said he was not upset by the launch.

North Korea state news agency KCNA quoted Kim as saying: "We cannot but develop nonstop super-powerful weapon systems to remove the potential and direct threats to the security of our country that exist in the south."

An official at Seoul's defence ministry said the missiles were believed to be a new type of short-range ballistic missile, an assessment echoed on Friday by the U.S.-South Korea Combined Forces Command (CFC).

A joint review with the United States showed both missiles flew some 600 km (373 miles), further than similar previous missile tests, the defence official told Reuters.

The official also said the missiles bore features similar to Russia' SS-26 Iskander and others the North tested in May - a relatively small, fast missile that experts say is easier to hide, launch and manoeuvre in flight.

A spokesman for the CFC said in a statement the launches were "not a threat directed at [South Korea] or the U.S., and have no impact on our defence posture."

Pyongyang has shown increasing frustration via state media that South Korea has not delivered promised economic cooperation or peace agreements but has imported F-35 stealth jet fighters and conducted military drills with the United States.

The KCNA report did not mention Trump or the United States, but said Kim criticised South Korean authorities for staging joint military exercises, which Trump promised to end after his first meeting with Kim in June 2018.

North Korea accused Washington of breaking that promise by planning to hold joint military exercises with South Korea next month and warned of a possible end to its freeze in nuclear and long-range missile tests.

While Friday's message was clearly directed at Seoul, it also sends signals to Washington, said Jenny Town, managing editor at 38 North, a project that studies North Korea.

"On some level, this is like North Korea's version of maximum pressure on South Korea and the United States."

'SOLEMN WARNING'

North Korean state newspaper Rodong Sinmun showed photos of the missile launching, Kim Jong Un looking through binoculars and at screens appearing to show the missile trajectory, and smiling and clapping with his officials.

Kim said the test was "a solemn warning to the south Korean military warmongers" and accused South Korean leaders of "double dealing" for saying they support peace while importing weapons and conducting military drills.

South Korean officials should stop such "suicidal acts" and "should not make a mistake of ignoring the warning," Kim said.

Kim said the rapid response and low-altitude trajectory of the weapon would make it difficult to intercept.

Jeffrey Lewis, a missile researcher at the James Martin Center for Nonproliferation Studies (CNS), said North Korea may have modified its missiles since the May test, based on initial photos and the distances.

Kim Dong-yup, a former naval officer who teaches at Seoul's Kyungnam University, said the North could have launched the same weapon as May but from the maximum firing angle this time.

"The latest launch has more political purposes as the North called it a show of force rather than firing drills like before, targeting the South's weapons purchases and joint exercises with the United States," Kim said.

Ballistic missile tests by North Korea are banned by U.N. Security Council resolutions that Pyongyang rejects as infringing on its right to self-defence.

U.S. Secretary of State Mike Pompeo told Fox News that fresh talks were still possible.